1. Field of the Invention
The invention lies in the field of nuclear magnetic resonance imaging (MRI) technology and particularly relates to the use of non-metallic support apparatus for surface coils in connection with such technology.
2. Description of Related Art
Nuclear magnetic resonance imaging is a recently developed art useful in the field of medical diagnosis, and is described for example in Valk et al., Basic Principles of Nuclear Magnetic Resonance Imaging, 1985, published by Elsevier Science Publishing Company, Inc., 52 Vanderbilt Avenue, New York, NY 10017 and numerous other publications. The basic technique requires a permanent magnetic field having a gradient and an RF magnetic field. A body to be imaged is scanned by switching the magnetic fields in both space and time using the well-known spin-echo effect. While the same radio frequency (RF) coil has been used to both transmit the RF magnetic field and to receive the spin-echo return signal, an improvement in image quality of small body areas has been achieved with the recent introduction of small surface coils. The surface coils receive the return signal instead of the RF coils. See for example pages 106 through 108 of the above-referenced text by Valk et al., and Zlatin et al., "Magnetic Resonance Imaging of the Shoulder", Magnetic Resonance Ouarterly, Volume 5, No. 1, pp. 3-22, January, 1989. As illustrated in the foregoing publication by Zlatin et al., a doughnut shaped surface coil is placed close to the body portion to be imaged. The coil is connected to an MRI system which performs the imaging processing and produces the images.
One MRI system currently in use is the 0.5 Tesla General Electric Magnetic Resonance Imaging System (also known as the 0.5 T GE MRI System) available from the General Electric Company, Fairfield, Connecticut, USA. A more robust MRI system now in use is the 1.5 Tesla General Electric Magnetic Resonance Imaging System (also known as the 1.5 T GE MRI System). The quality of the images obtained using MRI determines their usefulness in making a diagnosis.
Image quality is directly affected by placement of the surface coil. The coil must be held perfectly still and close to the body portion which is to be imaged. Moreover, the surface coil must be held at a particular angle with respect to the body and with respect to the MRI system in order to accomodate a particular angle of view which is required in each particular case. Prior to the introduction of the surface coil, clinical applications of MRI have been mostly for imaging the head or the spine, since the head and spine do not generally require an oblique angle of view with respect to the patient's body or with respect to the MRI system.
Applying MRI using conventional techniques to other body parts, such as the shoulder for example, results in lower quality images which are not as useful for diagnosis. Nevertheless, an interest is now developing in applying MRI to the shoulder, as evidenced by the above-cited publication by Zlatin et al. The Zlatin et al. publication is exemplary of one type of conventional technique for placing and supporting the surface coil in obtaining shoulder images with MRI. The apparatus illustrated in the Zlatin et al. publication for supporting the surface coils is narrowly and specifically designed for use in obtaining shoulder images or the like. The patient is forced to rest the shoulder of interest on top of the bottom surface coil, while a top surface coil is held over the same shoulder. In many cases, holding the patient in the supine position illustrated in the Zlatin et al. publication while resting the shoulder on one of the surface coils may be painful, particularly if the shoulder is injured, and the whole procedure may be somewhat impractical or excessively time consuming in certain cases. Moreover, it would seem a different apparatus for holding the surface coil would have to be designed for obtaining MRI images of body parts other than the shoulder, particularly if unique viewing angles are required.
Another example of a support apparatus for the surface coil having narrow applicability--for obtaining MRI images of the head only--is illustrated in a sheet entitled "Application Tips" distributed by General Electric Company in connection with its 0.5 T GE MRI System mentioned above, in which a technique is described for supporting the surface coil on a head rest.
There are certain restrictions in accommodating the patient's comfort while taking MRI images. For example, using a single surface coil to obtain shoulder images produces poorer quality images, particularly if the surface coil is located behind the shoulder. This is probably due to the larger amount of tissue near the back side of the shoulder. In view of this and various practical limitations, it has not seemed possible to improve the efficiency or to reduce patient discomfort in clinical MRI applications. More importantly, taking MRI images of other body portions (for example, hips, internal auditory canals, orbits, tempro mandibular joints, shoulders, etc.) involves significant inefficiencies. This is because in many cases a different support apparatus for the surface coil must be obtained or designed and then carefully installed with the patient in position. The different support apparatus must be specifically adapted to obtaining MRI images of the particular body portion of interest. Such a change in surface coil support apparatus represents a serious delay in a typical MRI clinic and inconvenience or discomfort for the patient.
In summary, obtaining MRI images requires an exacting effort in positioning the patient in the optimum position with respect to the MRI apparatus and then steadying a surface coil at just the right location and orientation with respect to the patient's shoulder or foot or hip, etc. Accordingly, most current clinical use is generally directed to imaging the head and spine or other "symmetrical" body part, since it does not seem possible to consistently obtain high quality MRI images of other body portions in the typical everyday clinical setting. Moreover, current practice must subordinate the patient's comfort to the exacting requirements of obtaining an MRI image.
Accordingly, there exists a great need to enable the typical MRI clinic to obtain MRI images of any and all body portions with the same efficiency while meeting the exacting requirements for obtaining high quality MRI images and without subordinating the patient's comfort to the degree previously required.